While acupuncture has been shown to be effective for chronic low back pain (cLBP) in many clinical trials, there is a current state of uncertainty as to why acupuncture is effective. In multiple trials, acupuncture does not demonstrate significant improvement over placebo controls based on sham needling, which can involve insertive or non-insertive "needling" with a device that presses against the skin. However, the use of sham needling as placebo control has been criticized since it may be an active therapy akin to acupressure. Ultimately, this state of uncertainty arising from acupuncture clinical trials exists because we lack understanding about the mechanisms of action underlying real versus various forms of sham acupuncture. Specifically, we do not know just how important needle insertion and somatosensory afference are to the mechanisms underlying acupuncture analgesia in cLBP. There is reason to believe that real acupuncture may have different mechanisms from sham acupuncture, and we propose that neuroimaging can inform a testable neurobiological model that identifies diverse mechanisms of action for acupuncture therapy with versus without somatosensory afference. These hypotheses will be tested on a specific chronic pain population, idiopathic cLBP, which has a significant "central" pain component characterized by aberrant somatotopy and augmented brain response to experimental pain (hyperalgesia). The brain correlates of clinical pain in cLBP have been less well characterized, but our own data suggests that clinical pain is associated with increased intrinsic functional connectivity between pain processing brain regions (e.g insula) and specific intrinsic connectivity networks. These networks include the executive attention network (EAN) and "default mode network" (DMN), a network thought to underlie self-referential cognition and modulated by acupuncture. We propose that real and different forms of sham acupuncture differentially modulate these networks, and alter somatotopy. Our overall goal is to evaluate whether the brain neurocircuitry subserving cLBP responds differentially to real versus "sham" acupuncture with and without somatosensory afference. To test our specific hypotheses, we will employ functional magnetic resonance imaging (fMRI) to assess brain networks subserving both clinical and experimental pain, acupuncture stimulation, and somatotopy in cLBP patients. These measures will be performed at baseline and following 7 weeks of (a.) acupuncture, ACUP;(b.) sham acupuncture with somatosensation, SHAM-sn;(c.) sham acupuncture without somatosensation, SHAM-ml\ or (d.) wait list, WL. Aim 1 will characterize the pain neurocircuitry in cLBP, as well as low back SI somatotopy, and brain response to acupuncture stimuli. Aim 2 will evaluate longitudinal effects of ACUP vs. SHAM-sn on brain networks and SI somatotopy in cLBP, while Aim 3 will evaluate the longitudinal effects of SHAM-sn vs. SHAM-ml on these same neuroimaging markers. Understanding the neural influence of somatosensation on acupuncture placebo effects will significantly impact our understanding of acupuncture and allow for development of more inert acupuncture placebos.